A colony of cotton-top tamarins (Saguinus oedipus oedipus) is maintained under NCI contract by ORAU to provide NCI research grant participants with a non-human primate model for viral and cancer research. However, because the cotton-top tamarin is an endangered species, its continued use by NCI grantees, as well as its development as a colon cancer model, is dependent upon successful reproduction by colony-born animals. While improvements in diet, husbandry and housing have greatly increased reproduction in imported females, the mortality rate of offspring of colony-born females is still around 80%. Evidence from the ORAU colony, as well as others, indicates that colony-born tamarins frequently abuse or neglect their infants. The purpose of the proposed research is to identify some of the determinants of reproductive competence in colony-born tamarin females. The results will aid in defining optimal age and social experience needed for successful rearing of young. Twenty-four cotton-top tamarin females will be used to examine the role of exposure to infant siblings under varying conditions in determining the display of adequate maternal behavior, with exposure defined as being housed with infant siblings during their first month of life. Subjects will be placed in one of four treatment groups: (1) exposure to infant siblings when immature, no previous exposure; (2) exposure when immature, previous exposure; (3) exposure when mature, no previous exposure; (4) exposure when mature, previous exposure. Each female's maturation state will be determined by regular measures of plasma ovarian steroid levels. The interactions of females with their infant siblings and subsequently with their own offspring will be quantitated. Results will be analyzed to determine the following: (a) Do sexual maturity and prior exposure to a previous litter increase the frequency of a female's interactions with infant siblings?; (b) Is the type and frequency of a female's interactions with her infant siblings related to her maternal performance? Determination of the effects of prior exposure and sexual maturity on a female's interactions with siblings will allow for prediction of the type of rearing experience a female with a particular family history has. The understanding of the relation between a female's experience with infant siblings and her subsequent maternal behavior will provide a basis for deciding upon the optimal age and past experience for potential breeders.